The ability of antisera from animals hyperimmunized against rough gram-negative bacteria to passively protect against purified endotoxins derived from heterologous gram-negative bacteria has been quantitated and shown to exist, but to be of a low order of magnitude. The ability of such antisera to protect against gram-negative bacterial sepsis will continue to be explored. Specifically, the ability of antisera from animals hyperimmunized with rough (RE) mutants of a variety of gram-negative bacteria will be assessed for their ability to transfer protection against challenge with heterologous gram-negative bacteria. The extent of such protection will be quantitated and compared with "O" specific antibody protection. The ability of these antisera to rough bacteria to protect when administered after the infection is in progress will also continue to be carefully quantitated so as to determine its potential value as a therapeutic (as contrasted to a prophylactic) agent in gram-negative bacterial sepsis.